<?php
/**
 * PHPExcel
 *
 * Copyright (c) 2006 - 2013 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * @category   PHPExcel
 * @package    PHPExcel_Writer_Excel5
 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt	LGPL
 * @version    1.7.9, 2013-06-02
 */

// Original file header of PEAR::Spreadsheet_Excel_Writer_Parser (used as the base for this class):
// -----------------------------------------------------------------------------------------
// *  Class for parsing Excel formulas
// *
// *  License Information:
// *
// *    Spreadsheet_Excel_Writer:  A library for generating Excel Spreadsheets
// *    Copyright (c) 2002-2003 Xavier Noguer xnoguer@rezebra.com
// *
// *    This library is free software; you can redistribute it and/or
// *    modify it under the terms of the GNU Lesser General Public
// *    License as published by the Free Software Foundation; either
// *    version 2.1 of the License, or (at your option) any later version.
// *
// *    This library is distributed in the hope that it will be useful,
// *    but WITHOUT ANY WARRANTY; without even the implied warranty of
// *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// *    Lesser General Public License for more details.
// *
// *    You should have received a copy of the GNU Lesser General Public
// *    License along with this library; if not, write to the Free Software
// *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
// */


/**
 * PHPExcel_Writer_Excel5_Parser
 *
 * @category   PHPExcel
 * @package    PHPExcel_Writer_Excel5
 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 */
class PHPExcel_Writer_Excel5_Parser {
	/**    Constants                */
	// Sheet title in unquoted form
	// Invalid sheet title characters cannot occur in the sheet title:
	// 		*:/\?[]
	// Moreover, there are valid sheet title characters that cannot occur in unquoted form (there may be more?)
	// +-% '^&<>=,;#()"{}
	const REGEX_SHEET_TITLE_UNQUOTED = '[^\*\:\/\\\\\?\[\]\+\-\% \\\'\^\&\<\>\=\,\;\#\(\)\"\{\}]+';

	// Sheet title in quoted form (without surrounding quotes)
	// Invalid sheet title characters cannot occur in the sheet title:
	// *:/\?[]					(usual invalid sheet title characters)
	// Single quote is represented as a pair ''
	const REGEX_SHEET_TITLE_QUOTED = '(([^\*\:\/\\\\\?\[\]\\\'])+|(\\\'\\\')+)+';

	/**
	 * The index of the character we are currently looking at
	 *
	 * @var integer
	 */
	public $_current_char;

	/**
	 * The token we are working on.
	 *
	 * @var string
	 */
	public $_current_token;

	/**
	 * The formula to parse
	 *
	 * @var string
	 */
	public $_formula;

	/**
	 * The character ahead of the current char
	 *
	 * @var string
	 */
	public $_lookahead;

	/**
	 * The parse tree to be generated
	 *
	 * @var string
	 */
	public $_parse_tree;

	/**
	 * Array of external sheets
	 *
	 * @var array
	 */
	public $_ext_sheets;

	/**
	 * Array of sheet references in the form of REF structures
	 *
	 * @var array
	 */
	public $_references;

	/**
	 * The class constructor
	 *
	 */
	public function __construct() {
		$this->_current_char = 0;
		$this->_current_token = ''; // The token we are working on.
		$this->_formula = ''; // The formula to parse.
		$this->_lookahead = ''; // The character ahead of the current char.
		$this->_parse_tree = ''; // The parse tree to be generated.
		$this->_initializeHashes(); // Initialize the hashes: ptg's and function's ptg's
		$this->_ext_sheets = array();
		$this->_references = array();
	}

	/**
	 * Initialize the ptg and function hashes.
	 *
	 * @access private
	 */
	function _initializeHashes() {
		// The Excel ptg indices
		$this->ptg = array(
				'ptgExp' => 0x01,
				'ptgTbl' => 0x02,
				'ptgAdd' => 0x03,
				'ptgSub' => 0x04,
				'ptgMul' => 0x05,
				'ptgDiv' => 0x06,
				'ptgPower' => 0x07,
				'ptgConcat' => 0x08,
				'ptgLT' => 0x09,
				'ptgLE' => 0x0A,
				'ptgEQ' => 0x0B,
				'ptgGE' => 0x0C,
				'ptgGT' => 0x0D,
				'ptgNE' => 0x0E,
				'ptgIsect' => 0x0F,
				'ptgUnion' => 0x10,
				'ptgRange' => 0x11,
				'ptgUplus' => 0x12,
				'ptgUminus' => 0x13,
				'ptgPercent' => 0x14,
				'ptgParen' => 0x15,
				'ptgMissArg' => 0x16,
				'ptgStr' => 0x17,
				'ptgAttr' => 0x19,
				'ptgSheet' => 0x1A,
				'ptgEndSheet' => 0x1B,
				'ptgErr' => 0x1C,
				'ptgBool' => 0x1D,
				'ptgInt' => 0x1E,
				'ptgNum' => 0x1F,
				'ptgArray' => 0x20,
				'ptgFunc' => 0x21,
				'ptgFuncVar' => 0x22,
				'ptgName' => 0x23,
				'ptgRef' => 0x24,
				'ptgArea' => 0x25,
				'ptgMemArea' => 0x26,
				'ptgMemErr' => 0x27,
				'ptgMemNoMem' => 0x28,
				'ptgMemFunc' => 0x29,
				'ptgRefErr' => 0x2A,
				'ptgAreaErr' => 0x2B,
				'ptgRefN' => 0x2C,
				'ptgAreaN' => 0x2D,
				'ptgMemAreaN' => 0x2E,
				'ptgMemNoMemN' => 0x2F,
				'ptgNameX' => 0x39,
				'ptgRef3d' => 0x3A,
				'ptgArea3d' => 0x3B,
				'ptgRefErr3d' => 0x3C,
				'ptgAreaErr3d' => 0x3D,
				'ptgArrayV' => 0x40,
				'ptgFuncV' => 0x41,
				'ptgFuncVarV' => 0x42,
				'ptgNameV' => 0x43,
				'ptgRefV' => 0x44,
				'ptgAreaV' => 0x45,
				'ptgMemAreaV' => 0x46,
				'ptgMemErrV' => 0x47,
				'ptgMemNoMemV' => 0x48,
				'ptgMemFuncV' => 0x49,
				'ptgRefErrV' => 0x4A,
				'ptgAreaErrV' => 0x4B,
				'ptgRefNV' => 0x4C,
				'ptgAreaNV' => 0x4D,
				'ptgMemAreaNV' => 0x4E,
				'ptgMemNoMemN' => 0x4F,
				'ptgFuncCEV' => 0x58,
				'ptgNameXV' => 0x59,
				'ptgRef3dV' => 0x5A,
				'ptgArea3dV' => 0x5B,
				'ptgRefErr3dV' => 0x5C,
				'ptgAreaErr3d' => 0x5D,
				'ptgArrayA' => 0x60,
				'ptgFuncA' => 0x61,
				'ptgFuncVarA' => 0x62,
				'ptgNameA' => 0x63,
				'ptgRefA' => 0x64,
				'ptgAreaA' => 0x65,
				'ptgMemAreaA' => 0x66,
				'ptgMemErrA' => 0x67,
				'ptgMemNoMemA' => 0x68,
				'ptgMemFuncA' => 0x69,
				'ptgRefErrA' => 0x6A,
				'ptgAreaErrA' => 0x6B,
				'ptgRefNA' => 0x6C,
				'ptgAreaNA' => 0x6D,
				'ptgMemAreaNA' => 0x6E,
				'ptgMemNoMemN' => 0x6F,
				'ptgFuncCEA' => 0x78,
				'ptgNameXA' => 0x79,
				'ptgRef3dA' => 0x7A,
				'ptgArea3dA' => 0x7B,
				'ptgRefErr3dA' => 0x7C,
				'ptgAreaErr3d' => 0x7D
		);

		// Thanks to Michael Meeks and Gnumeric for the initial arg values.
		//
		// The following hash was generated by "function_locale.pl" in the distro.
		// Refer to function_locale.pl for non-English function names.
		//
		// The array elements are as follow:
		// ptg:   The Excel function ptg code.
		// args:  The number of arguments that the function takes:
		//           >=0 is a fixed number of arguments.
		//           -1  is a variable  number of arguments.
		// class: The reference, value or array class of the function args.
		// vol:   The function is volatile.
		//
		$this->_functions = array(
			// function                  ptg  args  class  vol
			'COUNT' => array(0, -1, 0, 0),
			'IF' => array(1, -1, 1, 0),
			'ISNA' => array(2, 1, 1, 0),
			'ISERROR' => array(3, 1, 1, 0),
			'SUM' => array(4, -1, 0, 0),
			'AVERAGE' => array(5, -1, 0, 0),
			'MIN' => array(6, -1, 0, 0),
			'MAX' => array(7, -1, 0, 0),
			'ROW' => array(8, -1, 0, 0),
			'COLUMN' => array(9, -1, 0, 0),
			'NA' => array(10, 0, 0, 0),
			'NPV' => array(11, -1, 1, 0),
			'STDEV' => array(12, -1, 0, 0),
			'DOLLAR' => array(13, -1, 1, 0),
			'FIXED' => array(14, -1, 1, 0),
			'SIN' => array(15, 1, 1, 0),
			'COS' => array(16, 1, 1, 0),
			'TAN' => array(17, 1, 1, 0),
			'ATAN' => array(18, 1, 1, 0),
			'PI' => array(19, 0, 1, 0),
			'SQRT' => array(20, 1, 1, 0),
			'EXP' => array(21, 1, 1, 0),
			'LN' => array(22, 1, 1, 0),
			'LOG10' => array(23, 1, 1, 0),
			'ABS' => array(24, 1, 1, 0),
			'INT' => array(25, 1, 1, 0),
			'SIGN' => array(26, 1, 1, 0),
			'ROUND' => array(27, 2, 1, 0),
			'LOOKUP' => array(28, -1, 0, 0),
			'INDEX' => array(29, -1, 0, 1),
			'REPT' => array(30, 2, 1, 0),
			'MID' => array(31, 3, 1, 0),
			'LEN' => array(32, 1, 1, 0),
			'VALUE' => array(33, 1, 1, 0),
			'TRUE' => array(34, 0, 1, 0),
			'FALSE' => array(35, 0, 1, 0),
			'AND' => array(36, -1, 0, 0),
			'OR' => array(37, -1, 0, 0),
			'NOT' => array(38, 1, 1, 0),
			'MOD' => array(39, 2, 1, 0),
			'DCOUNT' => array(40, 3, 0, 0),
			'DSUM' => array(41, 3, 0, 0),
			'DAVERAGE' => array(42, 3, 0, 0),
			'DMIN' => array(43, 3, 0, 0),
			'DMAX' => array(44, 3, 0, 0),
			'DSTDEV' => array(45, 3, 0, 0),
			'VAR' => array(46, -1, 0, 0),
			'DVAR' => array(47, 3, 0, 0),
			'TEXT' => array(48, 2, 1, 0),
			'LINEST' => array(49, -1, 0, 0),
			'TREND' => array(50, -1, 0, 0),
			'LOGEST' => array(51, -1, 0, 0),
			'GROWTH' => array(52, -1, 0, 0),
			'PV' => array(56, -1, 1, 0),
			'FV' => array(57, -1, 1, 0),
			'NPER' => array(58, -1, 1, 0),
			'PMT' => array(59, -1, 1, 0),
			'RATE' => array(60, -1, 1, 0),
			'MIRR' => array(61, 3, 0, 0),
			'IRR' => array(62, -1, 0, 0),
			'RAND' => array(63, 0, 1, 1),
			'MATCH' => array(64, -1, 0, 0),
			'DATE' => array(65, 3, 1, 0),
			'TIME' => array(66, 3, 1, 0),
			'DAY' => array(67, 1, 1, 0),
			'MONTH' => array(68, 1, 1, 0),
			'YEAR' => array(69, 1, 1, 0),
			'WEEKDAY' => array(70, -1, 1, 0),
			'HOUR' => array(71, 1, 1, 0),
			'MINUTE' => array(72, 1, 1, 0),
			'SECOND' => array(73, 1, 1, 0),
			'NOW' => array(74, 0, 1, 1),
			'AREAS' => array(75, 1, 0, 1),
			'ROWS' => array(76, 1, 0, 1),
			'COLUMNS' => array(77, 1, 0, 1),
			'OFFSET' => array(78, -1, 0, 1),
			'SEARCH' => array(82, -1, 1, 0),
			'TRANSPOSE' => array(83, 1, 1, 0),
			'TYPE' => array(86, 1, 1, 0),
			'ATAN2' => array(97, 2, 1, 0),
			'ASIN' => array(98, 1, 1, 0),
			'ACOS' => array(99, 1, 1, 0),
			'CHOOSE' => array(100, -1, 1, 0),
			'HLOOKUP' => array(101, -1, 0, 0),
			'VLOOKUP' => array(102, -1, 0, 0),
			'ISREF' => array(105, 1, 0, 0),
			'LOG' => array(109, -1, 1, 0),
			'CHAR' => array(111, 1, 1, 0),
			'LOWER' => array(112, 1, 1, 0),
			'UPPER' => array(113, 1, 1, 0),
			'PROPER' => array(114, 1, 1, 0),
			'LEFT' => array(115, -1, 1, 0),
			'RIGHT' => array(116, -1, 1, 0),
			'EXACT' => array(117, 2, 1, 0),
			'TRIM' => array(118, 1, 1, 0),
			'REPLACE' => array(119, 4, 1, 0),
			'SUBSTITUTE' => array(120, -1, 1, 0),
			'CODE' => array(121, 1, 1, 0),
			'FIND' => array(124, -1, 1, 0),
			'CELL' => array(125, -1, 0, 1),
			'ISERR' => array(126, 1, 1, 0),
			'ISTEXT' => array(127, 1, 1, 0),
			'ISNUMBER' => array(128, 1, 1, 0),
			'ISBLANK' => array(129, 1, 1, 0),
			'T' => array(130, 1, 0, 0),
			'N' => array(131, 1, 0, 0),
			'DATEVALUE' => array(140, 1, 1, 0),
			'TIMEVALUE' => array(141, 1, 1, 0),
			'SLN' => array(142, 3, 1, 0),
			'SYD' => array(143, 4, 1, 0),
			'DDB' => array(144, -1, 1, 0),
			'INDIRECT' => array(148, -1, 1, 1),
			'CALL' => array(150, -1, 1, 0),
			'CLEAN' => array(162, 1, 1, 0),
			'MDETERM' => array(163, 1, 2, 0),
			'MINVERSE' => array(164, 1, 2, 0),
			'MMULT' => array(165, 2, 2, 0),
			'IPMT' => array(167, -1, 1, 0),
			'PPMT' => array(168, -1, 1, 0),
			'COUNTA' => array(169, -1, 0, 0),
			'PRODUCT' => array(183, -1, 0, 0),
			'FACT' => array(184, 1, 1, 0),
			'DPRODUCT' => array(189, 3, 0, 0),
			'ISNONTEXT' => array(190, 1, 1, 0),
			'STDEVP' => array(193, -1, 0, 0),
			'VARP' => array(194, -1, 0, 0),
			'DSTDEVP' => array(195, 3, 0, 0),
			'DVARP' => array(196, 3, 0, 0),
			'TRUNC' => array(197, -1, 1, 0),
			'ISLOGICAL' => array(198, 1, 1, 0),
			'DCOUNTA' => array(199, 3, 0, 0),
			'USDOLLAR' => array(204, -1, 1, 0),
			'FINDB' => array(205, -1, 1, 0),
			'SEARCHB' => array(206, -1, 1, 0),
			'REPLACEB' => array(207, 4, 1, 0),
			'LEFTB' => array(208, -1, 1, 0),
			'RIGHTB' => array(209, -1, 1, 0),
			'MIDB' => array(210, 3, 1, 0),
			'LENB' => array(211, 1, 1, 0),
			'ROUNDUP' => array(212, 2, 1, 0),
			'ROUNDDOWN' => array(213, 2, 1, 0),
			'ASC' => array(214, 1, 1, 0),
			'DBCS' => array(215, 1, 1, 0),
			'RANK' => array(216, -1, 0, 0),
			'ADDRESS' => array(219, -1, 1, 0),
			'DAYS360' => array(220, -1, 1, 0),
			'TODAY' => array(221, 0, 1, 1),
			'VDB' => array(222, -1, 1, 0),
			'MEDIAN' => array(227, -1, 0, 0),
			'SUMPRODUCT' => array(228, -1, 2, 0),
			'SINH' => array(229, 1, 1, 0),
			'COSH' => array(230, 1, 1, 0),
			'TANH' => array(231, 1, 1, 0),
			'ASINH' => array(232, 1, 1, 0),
			'ACOSH' => array(233, 1, 1, 0),
			'ATANH' => array(234, 1, 1, 0),
			'DGET' => array(235, 3, 0, 0),
			'INFO' => array(244, 1, 1, 1),
			'DB' => array(247, -1, 1, 0),
			'FREQUENCY' => array(252, 2, 0, 0),
			'ERROR.TYPE' => array(261, 1, 1, 0),
			'REGISTER.ID' => array(267, -1, 1, 0),
			'AVEDEV' => array(269, -1, 0, 0),
			'BETADIST' => array(270, -1, 1, 0),
			'GAMMALN' => array(271, 1, 1, 0),
			'BETAINV' => array(272, -1, 1, 0),
			'BINOMDIST' => array(273, 4, 1, 0),
			'CHIDIST' => array(274, 2, 1, 0),
			'CHIINV' => array(275, 2, 1, 0),
			'COMBIN' => array(276, 2, 1, 0),
			'CONFIDENCE' => array(277, 3, 1, 0),
			'CRITBINOM' => array(278, 3, 1, 0),
			'EVEN' => array(279, 1, 1, 0),
			'EXPONDIST' => array(280, 3, 1, 0),
			'FDIST' => array(281, 3, 1, 0),
			'FINV' => array(282, 3, 1, 0),
			'FISHER' => array(283, 1, 1, 0),
			'FISHERINV' => array(284, 1, 1, 0),
			'FLOOR' => array(285, 2, 1, 0),
			'GAMMADIST' => array(286, 4, 1, 0),
			'GAMMAINV' => array(287, 3, 1, 0),
			'CEILING' => array(288, 2, 1, 0),
			'HYPGEOMDIST' => array(289, 4, 1, 0),
			'LOGNORMDIST' => array(290, 3, 1, 0),
			'LOGINV' => array(291, 3, 1, 0),
			'NEGBINOMDIST' => array(292, 3, 1, 0),
			'NORMDIST' => array(293, 4, 1, 0),
			'NORMSDIST' => array(294, 1, 1, 0),
			'NORMINV' => array(295, 3, 1, 0),
			'NORMSINV' => array(296, 1, 1, 0),
			'STANDARDIZE' => array(297, 3, 1, 0),
			'ODD' => array(298, 1, 1, 0),
			'PERMUT' => array(299, 2, 1, 0),
			'POISSON' => array(300, 3, 1, 0),
			'TDIST' => array(301, 3, 1, 0),
			'WEIBULL' => array(302, 4, 1, 0),
			'SUMXMY2' => array(303, 2, 2, 0),
			'SUMX2MY2' => array(304, 2, 2, 0),
			'SUMX2PY2' => array(305, 2, 2, 0),
			'CHITEST' => array(306, 2, 2, 0),
			'CORREL' => array(307, 2, 2, 0),
			'COVAR' => array(308, 2, 2, 0),
			'FORECAST' => array(309, 3, 2, 0),
			'FTEST' => array(310, 2, 2, 0),
			'INTERCEPT' => array(311, 2, 2, 0),
			'PEARSON' => array(312, 2, 2, 0),
			'RSQ' => array(313, 2, 2, 0),
			'STEYX' => array(314, 2, 2, 0),
			'SLOPE' => array(315, 2, 2, 0),
			'TTEST' => array(316, 4, 2, 0),
			'PROB' => array(317, -1, 2, 0),
			'DEVSQ' => array(318, -1, 0, 0),
			'GEOMEAN' => array(319, -1, 0, 0),
			'HARMEAN' => array(320, -1, 0, 0),
			'SUMSQ' => array(321, -1, 0, 0),
			'KURT' => array(322, -1, 0, 0),
			'SKEW' => array(323, -1, 0, 0),
			'ZTEST' => array(324, -1, 0, 0),
			'LARGE' => array(325, 2, 0, 0),
			'SMALL' => array(326, 2, 0, 0),
			'QUARTILE' => array(327, 2, 0, 0),
			'PERCENTILE' => array(328, 2, 0, 0),
			'PERCENTRANK' => array(329, -1, 0, 0),
			'MODE' => array(330, -1, 2, 0),
			'TRIMMEAN' => array(331, 2, 0, 0),
			'TINV' => array(332, 2, 1, 0),
			'CONCATENATE' => array(336, -1, 1, 0),
			'POWER' => array(337, 2, 1, 0),
			'RADIANS' => array(342, 1, 1, 0),
			'DEGREES' => array(343, 1, 1, 0),
			'SUBTOTAL' => array(344, -1, 0, 0),
			'SUMIF' => array(345, -1, 0, 0),
			'COUNTIF' => array(346, 2, 0, 0),
			'COUNTBLANK' => array(347, 1, 0, 0),
			'ISPMT' => array(350, 4, 1, 0),
			'DATEDIF' => array(351, 3, 1, 0),
			'DATESTRING' => array(352, 1, 1, 0),
			'NUMBERSTRING' => array(353, 2, 1, 0),
			'ROMAN' => array(354, -1, 1, 0),
			'GETPIVOTDATA' => array(358, -1, 0, 0),
			'HYPERLINK' => array(359, -1, 1, 0),
			'PHONETIC' => array(360, 1, 0, 0),
			'AVERAGEA' => array(361, -1, 0, 0),
			'MAXA' => array(362, -1, 0, 0),
			'MINA' => array(363, -1, 0, 0),
			'STDEVPA' => array(364, -1, 0, 0),
			'VARPA' => array(365, -1, 0, 0),
			'STDEVA' => array(366, -1, 0, 0),
			'VARA' => array(367, -1, 0, 0),
			'BAHTTEXT' => array(368, 1, 0, 0),
		);
	}

	/**
	 * Convert a token to the proper ptg value.
	 *
	 * @access private
	 *
	 * @param mixed $token The token to convert.
	 *
	 * @return mixed the converted token on success
	 */
	function _convert($token) {
		if (preg_match("/\"([^\"]|\"\"){0,255}\"/", $token))
		{
			return $this->_convertString($token);

		}
		elseif (is_numeric($token))
		{
			return $this->_convertNumber($token);

			// match references like A1 or $A$1
		}
		elseif (preg_match('/^\$?([A-Ia-i]?[A-Za-z])\$?(\d+)$/', $token))
		{
			return $this->_convertRef2d($token);

			// match external references like Sheet1!A1 or Sheet1:Sheet2!A1 or Sheet1!$A$1 or Sheet1:Sheet2!$A$1
		}
		elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?[A-Ia-i]?[A-Za-z]\\$?(\d+)$/u", $token))
		{
			return $this->_convertRef3d($token);

			// match external references like 'Sheet1'!A1 or 'Sheet1:Sheet2'!A1 or 'Sheet1'!$A$1 or 'Sheet1:Sheet2'!$A$1
		}
		elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?[A-Ia-i]?[A-Za-z]\\$?(\d+)$/u", $token))
		{
			return $this->_convertRef3d($token);

			// match ranges like A1:B2 or $A$1:$B$2
		}
		elseif (preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?(\d+)\:(\$)?[A-Ia-i]?[A-Za-z](\$)?(\d+)$/', $token))
		{
			return $this->_convertRange2d($token);

			// match external ranges like Sheet1!A1:B2 or Sheet1:Sheet2!A1:B2 or Sheet1!$A$1:$B$2 or Sheet1:Sheet2!$A$1:$B$2
		}
		elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?([A-Ia-i]?[A-Za-z])?\\$?(\d+)\:\\$?([A-Ia-i]?[A-Za-z])?\\$?(\d+)$/u", $token))
		{
			return $this->_convertRange3d($token);

			// match external ranges like 'Sheet1'!A1:B2 or 'Sheet1:Sheet2'!A1:B2 or 'Sheet1'!$A$1:$B$2 or 'Sheet1:Sheet2'!$A$1:$B$2
		}
		elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?([A-Ia-i]?[A-Za-z])?\\$?(\d+)\:\\$?([A-Ia-i]?[A-Za-z])?\\$?(\d+)$/u", $token))
		{
			return $this->_convertRange3d($token);

			// operators (including parentheses)
		}
		elseif (isset($this->ptg[$token]))
		{
			return pack("C", $this->ptg[$token]);

			// match error codes
		}
		elseif (preg_match("/^#[A-Z0\/]{3,5}[!?]{1}$/", $token) or $token == '#N/A')
		{
			return $this->_convertError($token);

			// commented so argument number can be processed correctly. See toReversePolish().
			/*elseif (preg_match("/[A-Z0-9\xc0-\xdc\.]+/",$token))
			{
				return($this->_convertFunction($token,$this->_func_args));
			}*/

			// if it's an argument, ignore the token (the argument remains)
		}
		elseif ($token == 'arg')
		{
			return '';
		}

		// TODO: use real error codes
		throw new PHPExcel_Writer_Exception("Unknown token $token");
	}

	/**
	 * Convert a number token to ptgInt or ptgNum
	 *
	 * @access private
	 *
	 * @param mixed $num an integer or double for conversion to its ptg value
	 */
	function _convertNumber($num) {
		// Integer in the range 0..2**16-1
		if ((preg_match("/^\d+$/", $num)) and ($num <= 65535))
		{
			return pack("Cv", $this->ptg['ptgInt'], $num);
		}
		else
		{ // A float
			if (PHPExcel_Writer_Excel5_BIFFwriter::getByteOrder())
			{ // if it's Big Endian
				$num = strrev($num);
			}

			return pack("Cd", $this->ptg['ptgNum'], $num);
		}
	}

	/**
	 * Convert a string token to ptgStr
	 *
	 * @access private
	 *
	 * @param string $string A string for conversion to its ptg value.
	 *
	 * @return mixed the converted token on success
	 */
	function _convertString($string) {
		// chop away beggining and ending quotes
		$string = substr($string, 1, strlen($string) - 2);
		if (strlen($string) > 255)
		{
			throw new PHPExcel_Writer_Exception("String is too long");
		}

		return pack('C', $this->ptg['ptgStr']) . PHPExcel_Shared_String::UTF8toBIFF8UnicodeShort($string);
	}

	/**
	 * Convert a function to a ptgFunc or ptgFuncVarV depending on the number of
	 * args that it takes.
	 *
	 * @access private
	 *
	 * @param string  $token    The name of the function for convertion to ptg value.
	 * @param integer $num_args The number of arguments the function receives.
	 *
	 * @return string The packed ptg for the function
	 */
	function _convertFunction($token, $num_args) {
		$args = $this->_functions[$token][1];
		//		$volatile = $this->_functions[$token][3];

		// Fixed number of args eg. TIME($i,$j,$k).
		if ($args >= 0)
		{
			return pack("Cv", $this->ptg['ptgFuncV'], $this->_functions[$token][0]);
		}
		// Variable number of args eg. SUM($i,$j,$k, ..).
		if ($args == -1)
		{
			return pack("CCv", $this->ptg['ptgFuncVarV'], $num_args, $this->_functions[$token][0]);
		}
	}

	/**
	 * Convert an Excel range such as A1:D4 to a ptgRefV.
	 *
	 * @access private
	 *
	 * @param string $range An Excel range in the A1:A2
	 * @param int    $class
	 */
	function _convertRange2d($range, $class = 0) {

		// TODO: possible class value 0,1,2 check Formula.pm
		// Split the range into 2 cell refs
		if (preg_match('/^(\$)?([A-Ia-i]?[A-Za-z])(\$)?(\d+)\:(\$)?([A-Ia-i]?[A-Za-z])(\$)?(\d+)$/', $range))
		{
			list($cell1, $cell2) = explode(':', $range);
		}
		else
		{
			// TODO: use real error codes
			throw new PHPExcel_Writer_Exception("Unknown range separator");
		}

		// Convert the cell references
		list($row1, $col1) = $this->_cellToPackedRowcol($cell1);
		list($row2, $col2) = $this->_cellToPackedRowcol($cell2);

		// The ptg value depends on the class of the ptg.
		if ($class == 0)
		{
			$ptgArea = pack("C", $this->ptg['ptgArea']);
		}
		elseif ($class == 1)
		{
			$ptgArea = pack("C", $this->ptg['ptgAreaV']);
		}
		elseif ($class == 2)
		{
			$ptgArea = pack("C", $this->ptg['ptgAreaA']);
		}
		else
		{
			// TODO: use real error codes
			throw new PHPExcel_Writer_Exception("Unknown class $class");
		}

		return $ptgArea . $row1 . $row2 . $col1 . $col2;
	}

	/**
	 * Convert an Excel 3d range such as "Sheet1!A1:D4" or "Sheet1:Sheet2!A1:D4" to
	 * a ptgArea3d.
	 *
	 * @access private
	 *
	 * @param string $token An Excel range in the Sheet1!A1:A2 format.
	 *
	 * @return mixed The packed ptgArea3d token on success.
	 */
	function _convertRange3d($token) {
		//		$class = 0; // formulas like Sheet1!$A$1:$A$2 in list type data validation need this class (0x3B)

		// Split the ref at the ! symbol
		list($ext_ref, $range) = explode('!', $token);

		// Convert the external reference part (different for BIFF8)
		$ext_ref = $this->_getRefIndex($ext_ref);

		// Split the range into 2 cell refs
		list($cell1, $cell2) = explode(':', $range);

		// Convert the cell references
		if (preg_match("/^(\\$)?[A-Ia-i]?[A-Za-z](\\$)?(\d+)$/", $cell1))
		{
			list($row1, $col1) = $this->_cellToPackedRowcol($cell1);
			list($row2, $col2) = $this->_cellToPackedRowcol($cell2);
		}
		else
		{ // It's a rows range (like 26:27)
			list($row1, $col1, $row2, $col2) = $this->_rangeToPackedRange($cell1 . ':' . $cell2);
		}

		// The ptg value depends on the class of the ptg.
		//		if ($class == 0) {
		$ptgArea = pack("C", $this->ptg['ptgArea3d']);
		//		} elseif ($class == 1) {
		//			$ptgArea = pack("C", $this->ptg['ptgArea3dV']);
		//		} elseif ($class == 2) {
		//			$ptgArea = pack("C", $this->ptg['ptgArea3dA']);
		//		} else {
		//			throw new PHPExcel_Writer_Exception("Unknown class $class");
		//		}

		return $ptgArea . $ext_ref . $row1 . $row2 . $col1 . $col2;
	}

	/**
	 * Convert an Excel reference such as A1, $B2, C$3 or $D$4 to a ptgRefV.
	 *
	 * @access private
	 *
	 * @param string $cell An Excel cell reference
	 *
	 * @return string The cell in packed() format with the corresponding ptg
	 */
	function _convertRef2d($cell) {
		//		$class = 2; // as far as I know, this is magick.

		// Convert the cell reference
		$cell_array = $this->_cellToPackedRowcol($cell);
		list($row, $col) = $cell_array;

		// The ptg value depends on the class of the ptg.
		//		if ($class == 0) {
		//			$ptgRef = pack("C", $this->ptg['ptgRef']);
		//		} elseif ($class == 1) {
		//			$ptgRef = pack("C", $this->ptg['ptgRefV']);
		//		} elseif ($class == 2) {
		$ptgRef = pack("C", $this->ptg['ptgRefA']);
		//		} else {
		//			// TODO: use real error codes
		//			throw new PHPExcel_Writer_Exception("Unknown class $class");
		//		}
		return $ptgRef . $row . $col;
	}

	/**
	 * Convert an Excel 3d reference such as "Sheet1!A1" or "Sheet1:Sheet2!A1" to a
	 * ptgRef3d.
	 *
	 * @access private
	 *
	 * @param string $cell An Excel cell reference
	 *
	 * @return mixed The packed ptgRef3d token on success.
	 */
	function _convertRef3d($cell) {
		//		$class = 2; // as far as I know, this is magick.

		// Split the ref at the ! symbol
		list($ext_ref, $cell) = explode('!', $cell);

		// Convert the external reference part (different for BIFF8)
		$ext_ref = $this->_getRefIndex($ext_ref);

		// Convert the cell reference part
		list($row, $col) = $this->_cellToPackedRowcol($cell);

		// The ptg value depends on the class of the ptg.
		//		if ($class == 0) {
		//			$ptgRef = pack("C", $this->ptg['ptgRef3d']);
		//		} elseif ($class == 1) {
		//			$ptgRef = pack("C", $this->ptg['ptgRef3dV']);
		//		} elseif ($class == 2) {
		$ptgRef = pack("C", $this->ptg['ptgRef3dA']);
		//		} else {
		//			throw new PHPExcel_Writer_Exception("Unknown class $class");
		//		}

		return $ptgRef . $ext_ref . $row . $col;
	}

	/**
	 * Convert an error code to a ptgErr
	 *
	 * @access    private
	 *
	 * @param    string $errorCode The error code for conversion to its ptg value
	 *
	 * @return    string                The error code ptgErr
	 */
	function _convertError($errorCode) {
		switch ($errorCode)
		{
			case '#NULL!':
				return pack("C", 0x00);
			case '#DIV/0!':
				return pack("C", 0x07);
			case '#VALUE!':
				return pack("C", 0x0F);
			case '#REF!':
				return pack("C", 0x17);
			case '#NAME?':
				return pack("C", 0x1D);
			case '#NUM!':
				return pack("C", 0x24);
			case '#N/A':
				return pack("C", 0x2A);
		}
		return pack("C", 0xFF);
	}

	/**
	 * Convert the sheet name part of an external reference, for example "Sheet1" or
	 * "Sheet1:Sheet2", to a packed structure.
	 *
	 * @access    private
	 *
	 * @param    string $ext_ref The name of the external reference
	 *
	 * @return    string                The reference index in packed() format
	 */
	function _packExtRef($ext_ref) {
		$ext_ref = preg_replace("/^'/", '', $ext_ref); // Remove leading  ' if any.
		$ext_ref = preg_replace("/'$/", '', $ext_ref); // Remove trailing ' if any.

		// Check if there is a sheet range eg., Sheet1:Sheet2.
		if (preg_match("/:/", $ext_ref))
		{
			list($sheet_name1, $sheet_name2) = explode(':', $ext_ref);

			$sheet1 = $this->_getSheetIndex($sheet_name1);
			if ($sheet1 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $sheet_name1 in formula");
			}
			$sheet2 = $this->_getSheetIndex($sheet_name2);
			if ($sheet2 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $sheet_name2 in formula");
			}

			// Reverse max and min sheet numbers if necessary
			if ($sheet1 > $sheet2)
			{
				list($sheet1, $sheet2) = array($sheet2, $sheet1);
			}
		}
		else
		{ // Single sheet name only.
			$sheet1 = $this->_getSheetIndex($ext_ref);
			if ($sheet1 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $ext_ref in formula");
			}
			$sheet2 = $sheet1;
		}

		// References are stored relative to 0xFFFF.
		$offset = -1 - $sheet1;

		return pack('vdvv', $offset, 0x00, $sheet1, $sheet2);
	}

	/**
	 * Look up the REF index that corresponds to an external sheet name
	 * (or range). If it doesn't exist yet add it to the workbook's references
	 * array. It assumes all sheet names given must exist.
	 *
	 * @access private
	 *
	 * @param string $ext_ref The name of the external reference
	 *
	 * @return mixed The reference index in packed() format on success
	 */
	function _getRefIndex($ext_ref) {
		$ext_ref = preg_replace("/^'/", '', $ext_ref); // Remove leading  ' if any.
		$ext_ref = preg_replace("/'$/", '', $ext_ref); // Remove trailing ' if any.
		$ext_ref = str_replace('\'\'', '\'', $ext_ref); // Replace escaped '' with '

		// Check if there is a sheet range eg., Sheet1:Sheet2.
		if (preg_match("/:/", $ext_ref))
		{
			list($sheet_name1, $sheet_name2) = explode(':', $ext_ref);

			$sheet1 = $this->_getSheetIndex($sheet_name1);
			if ($sheet1 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $sheet_name1 in formula");
			}
			$sheet2 = $this->_getSheetIndex($sheet_name2);
			if ($sheet2 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $sheet_name2 in formula");
			}

			// Reverse max and min sheet numbers if necessary
			if ($sheet1 > $sheet2)
			{
				list($sheet1, $sheet2) = array($sheet2, $sheet1);
			}
		}
		else
		{ // Single sheet name only.
			$sheet1 = $this->_getSheetIndex($ext_ref);
			if ($sheet1 == -1)
			{
				throw new PHPExcel_Writer_Exception("Unknown sheet name $ext_ref in formula");
			}
			$sheet2 = $sheet1;
		}

		// assume all references belong to this document
		$supbook_index = 0x00;
		$ref = pack('vvv', $supbook_index, $sheet1, $sheet2);
		$total_references = count($this->_references);
		$index = -1;
		for ($i = 0; $i < $total_references; ++$i)
		{
			if ($ref == $this->_references[$i])
			{
				$index = $i;
				break;
			}
		}
		// if REF was not found add it to references array
		if ($index == -1)
		{
			$this->_references[$total_references] = $ref;
			$index = $total_references;
		}

		return pack('v', $index);
	}

	/**
	 * Look up the index that corresponds to an external sheet name. The hash of
	 * sheet names is updated by the addworksheet() method of the
	 * PHPExcel_Writer_Excel5_Workbook class.
	 *
	 * @access    private
	 *
	 * @param    string $sheet_name Sheet name
	 *
	 * @return    integer                    The sheet index, -1 if the sheet was not found
	 */
	function _getSheetIndex($sheet_name) {
		if (!isset($this->_ext_sheets[$sheet_name]))
		{
			return -1;
		}
		else
		{
			return $this->_ext_sheets[$sheet_name];
		}
	}

	/**
	 * This method is used to update the array of sheet names. It is
	 * called by the addWorksheet() method of the
	 * PHPExcel_Writer_Excel5_Workbook class.
	 *
	 * @access public
	 * @see    PHPExcel_Writer_Excel5_Workbook::addWorksheet()
	 *
	 * @param string  $name  The name of the worksheet being added
	 * @param integer $index The index of the worksheet being added
	 */
	function setExtSheet($name, $index) {
		$this->_ext_sheets[$name] = $index;
	}

	/**
	 * pack() row and column into the required 3 or 4 byte format.
	 *
	 * @access private
	 *
	 * @param string $cell The Excel cell reference to be packed
	 *
	 * @return array Array containing the row and column in packed() format
	 */
	function _cellToPackedRowcol($cell) {
		$cell = strtoupper($cell);
		list($row, $col, $row_rel, $col_rel) = $this->_cellToRowcol($cell);
		if ($col >= 256)
		{
			throw new PHPExcel_Writer_Exception("Column in: $cell greater than 255");
		}
		if ($row >= 65536)
		{
			throw new PHPExcel_Writer_Exception("Row in: $cell greater than 65536 ");
		}

		// Set the high bits to indicate if row or col are relative.
		$col |= $col_rel << 14;
		$col |= $row_rel << 15;
		$col = pack('v', $col);

		$row = pack('v', $row);

		return array($row, $col);
	}

	/**
	 * pack() row range into the required 3 or 4 byte format.
	 * Just using maximum col/rows, which is probably not the correct solution
	 *
	 * @access private
	 *
	 * @param string $range The Excel range to be packed
	 *
	 * @return array Array containing (row1,col1,row2,col2) in packed() format
	 */
	function _rangeToPackedRange($range) {
		preg_match('/(\$)?(\d+)\:(\$)?(\d+)/', $range, $match);
		// return absolute rows if there is a $ in the ref
		$row1_rel = empty($match[1]) ? 1 : 0;
		$row1 = $match[2];
		$row2_rel = empty($match[3]) ? 1 : 0;
		$row2 = $match[4];
		// Convert 1-index to zero-index
		--$row1;
		--$row2;
		// Trick poor inocent Excel
		$col1 = 0;
		$col2 = 65535; // FIXME: maximum possible value for Excel 5 (change this!!!)

		// FIXME: this changes for BIFF8
		if (($row1 >= 65536) or ($row2 >= 65536))
		{
			throw new PHPExcel_Writer_Exception("Row in: $range greater than 65536 ");
		}

		// Set the high bits to indicate if rows are relative.
		$col1 |= $row1_rel << 15;
		$col2 |= $row2_rel << 15;
		$col1 = pack('v', $col1);
		$col2 = pack('v', $col2);

		$row1 = pack('v', $row1);
		$row2 = pack('v', $row2);

		return array($row1, $col1, $row2, $col2);
	}

	/**
	 * Convert an Excel cell reference such as A1 or $B2 or C$3 or $D$4 to a zero
	 * indexed row and column number. Also returns two (0,1) values to indicate
	 * whether the row or column are relative references.
	 *
	 * @access private
	 *
	 * @param string $cell The Excel cell reference in A1 format.
	 *
	 * @return array
	 */
	function _cellToRowcol($cell) {
		preg_match('/(\$)?([A-I]?[A-Z])(\$)?(\d+)/', $cell, $match);
		// return absolute column if there is a $ in the ref
		$col_rel = empty($match[1]) ? 1 : 0;
		$col_ref = $match[2];
		$row_rel = empty($match[3]) ? 1 : 0;
		$row = $match[4];

		// Convert base26 column string to a number.
		$expn = strlen($col_ref) - 1;
		$col = 0;
		$col_ref_length = strlen($col_ref);
		for ($i = 0; $i < $col_ref_length; ++$i)
		{
			$col += (ord($col_ref{$i}) - 64) * pow(26, $expn);
			--$expn;
		}

		// Convert 1-index to zero-index
		--$row;
		--$col;

		return array($row, $col, $row_rel, $col_rel);
	}

	/**
	 * Advance to the next valid token.
	 *
	 * @access private
	 */
	function _advance() {
		$i = $this->_current_char;
		$formula_length = strlen($this->_formula);
		// eat up white spaces
		if ($i < $formula_length)
		{
			while ($this->_formula{$i} == " ")
			{
				++$i;
			}

			if ($i < ($formula_length - 1))
			{
				$this->_lookahead = $this->_formula{$i + 1};
			}
			$token = '';
		}

		while ($i < $formula_length)
		{
			$token .= $this->_formula{$i};

			if ($i < ($formula_length - 1))
			{
				$this->_lookahead = $this->_formula{$i + 1};
			}
			else
			{
				$this->_lookahead = '';
			}

			if ($this->_match($token) != '')
			{
				//if ($i < strlen($this->_formula) - 1) {
				//    $this->_lookahead = $this->_formula{$i+1};
				//}
				$this->_current_char = $i + 1;
				$this->_current_token = $token;

				return 1;
			}

			if ($i < ($formula_length - 2))
			{
				$this->_lookahead = $this->_formula{$i + 2};
			}
			else
			{ // if we run out of characters _lookahead becomes empty
				$this->_lookahead = '';
			}
			++$i;
		}
		//die("Lexical error ".$this->_current_char);
	}

	/**
	 * Checks if it's a valid token.
	 *
	 * @access private
	 *
	 * @param mixed $token The token to check.
	 *
	 * @return mixed       The checked token or false on failure
	 */
	function _match($token) {
		switch ($token)
		{
			case "+":
			case "-":
			case "*":
			case "/":
			case "(":
			case ")":
			case ",":
			case ";":
			case ">=":
			case "<=":
			case "=":
			case "<>":
			case "^":
			case "&":
			case "%":
				return $token;
				break;
			case ">":
				if ($this->_lookahead == '=')
				{ // it's a GE token
					break;
				}

				return $token;
				break;
			case "<":
				// it's a LE or a NE token
				if (($this->_lookahead == '=') or ($this->_lookahead == '>'))
				{
					break;
				}

				return $token;
				break;
			default:
				// if it's a reference A1 or $A$1 or $A1 or A$1
				if (preg_match('/^\$?[A-Ia-i]?[A-Za-z]\$?[0-9]+$/', $token) and !preg_match("/[0-9]/", $this->_lookahead) and ($this->_lookahead != ':') and ($this->_lookahead != '.') and ($this->_lookahead != '!'))
				{
					return $token;
				}
				// If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1 or Sheet1!$A$1 or Sheet1:Sheet2!$A$1)
				elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?[A-Ia-i]?[A-Za-z]\\$?[0-9]+$/u", $token) and !preg_match("/[0-9]/", $this->_lookahead) and ($this->_lookahead != ':') and ($this->_lookahead != '.'))
				{
					return $token;
				}
				// If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1 or 'Sheet1'!$A$1 or 'Sheet1:Sheet2'!$A$1)
				elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?[A-Ia-i]?[A-Za-z]\\$?[0-9]+$/u", $token) and !preg_match("/[0-9]/", $this->_lookahead) and ($this->_lookahead != ':') and ($this->_lookahead != '.'))
				{
					return $token;
				}
				// if it's a range A1:A2 or $A$1:$A$2
				elseif (preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+:(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+$/', $token) and !preg_match("/[0-9]/", $this->_lookahead))
				{
					return $token;
				}
				// If it's an external range like Sheet1!A1:B2 or Sheet1:Sheet2!A1:B2 or Sheet1!$A$1:$B$2 or Sheet1:Sheet2!$A$1:$B$2
				elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+:\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+$/u", $token) and !preg_match("/[0-9]/", $this->_lookahead))
				{
					return $token;
				}
				// If it's an external range like 'Sheet1'!A1:B2 or 'Sheet1:Sheet2'!A1:B2 or 'Sheet1'!$A$1:$B$2 or 'Sheet1:Sheet2'!$A$1:$B$2
				elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+:\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+$/u", $token) and !preg_match("/[0-9]/", $this->_lookahead))
				{
					return $token;
				}
				// If it's a number (check that it's not a sheet name or range)
				elseif (is_numeric($token) and (!is_numeric($token . $this->_lookahead) or ($this->_lookahead == '')) and ($this->_lookahead != '!') and ($this->_lookahead != ':'))
				{
					return $token;
				}
				// If it's a string (of maximum 255 characters)
				elseif (preg_match("/\"([^\"]|\"\"){0,255}\"/", $token) and $this->_lookahead != '"' and (substr_count($token, '"') % 2 == 0))
				{
					return $token;
				}
				// If it's an error code
				elseif (preg_match("/^#[A-Z0\/]{3,5}[!?]{1}$/", $token) or $token == '#N/A')
				{
					return $token;
				}
				// if it's a function call
				elseif (preg_match("/^[A-Z0-9\xc0-\xdc\.]+$/i", $token) and ($this->_lookahead == "("))
				{
					return $token;
				}
				//	It's an argument of some description (e.g. a named range),
				//		precise nature yet to be determined
				elseif (substr($token, -1) == ')')
				{
					return $token;
				}

				return '';
		}
	}

	/**
	 * The parsing method. It parses a formula.
	 *
	 * @access public
	 *
	 * @param string $formula The formula to parse, without the initial equal
	 *                        sign (=).
	 *
	 * @return mixed true on success
	 */
	function parse($formula) {
		$this->_current_char = 0;
		$this->_formula = $formula;
		$this->_lookahead = isset($formula{1}) ? $formula{1} : '';
		$this->_advance();
		$this->_parse_tree = $this->_condition();

		return true;
	}

	/**
	 * It parses a condition. It assumes the following rule:
	 * Cond -> Expr [(">" | "<") Expr]
	 *
	 * @access private
	 * @return mixed The parsed ptg'd tree on success
	 */
	function _condition() {
		$result = $this->_expression();
		if ($this->_current_token == "<")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgLT', $result, $result2);
		}
		elseif ($this->_current_token == ">")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgGT', $result, $result2);
		}
		elseif ($this->_current_token == "<=")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgLE', $result, $result2);
		}
		elseif ($this->_current_token == ">=")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgGE', $result, $result2);
		}
		elseif ($this->_current_token == "=")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgEQ', $result, $result2);
		}
		elseif ($this->_current_token == "<>")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgNE', $result, $result2);
		}
		elseif ($this->_current_token == "&")
		{
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgConcat', $result, $result2);
		}

		return $result;
	}

	/**
	 * It parses a expression. It assumes the following rule:
	 * Expr -> Term [("+" | "-") Term]
	 *      -> "string"
	 *      -> "-" Term : Negative value
	 *      -> "+" Term : Positive value
	 *      -> Error code
	 *
	 * @access private
	 * @return mixed The parsed ptg'd tree on success
	 */
	function _expression() {
		// If it's a string return a string node
		if (preg_match("/\"([^\"]|\"\"){0,255}\"/", $this->_current_token))
		{
			$tmp = str_replace('""', '"', $this->_current_token);
			if (($tmp == '"') || ($tmp == ''))
				$tmp = '""'; //	Trap for "" that has been used for an empty string
			$result = $this->_createTree($tmp, '', '');
			$this->_advance();

			return $result;
			// If it's an error code
		}
		elseif (preg_match("/^#[A-Z0\/]{3,5}[!?]{1}$/", $this->_current_token) or $this->_current_token == '#N/A')
		{
			$result = $this->_createTree($this->_current_token, 'ptgErr', '');
			$this->_advance();

			return $result;
			// If it's a negative value
		}
		elseif ($this->_current_token == "-")
		{
			// catch "-" Term
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgUminus', $result2, '');

			return $result;
			// If it's a positive value
		}
		elseif ($this->_current_token == "+")
		{
			// catch "+" Term
			$this->_advance();
			$result2 = $this->_expression();
			$result = $this->_createTree('ptgUplus', $result2, '');

			return $result;
		}
		$result = $this->_term();
		while (($this->_current_token == "+") or ($this->_current_token == "-") or ($this->_current_token == "^"))
		{
			/**/
			if ($this->_current_token == "+")
			{
				$this->_advance();
				$result2 = $this->_term();
				$result = $this->_createTree('ptgAdd', $result, $result2);
			}
			elseif ($this->_current_token == "-")
			{
				$this->_advance();
				$result2 = $this->_term();
				$result = $this->_createTree('ptgSub', $result, $result2);
			}
			else
			{
				$this->_advance();
				$result2 = $this->_term();
				$result = $this->_createTree('ptgPower', $result, $result2);
			}
		}

		return $result;
	}

	/**
	 * This function just introduces a ptgParen element in the tree, so that Excel
	 * doesn't get confused when working with a parenthesized formula afterwards.
	 *
	 * @access private
	 * @see    _fact()
	 * @return array The parsed ptg'd tree
	 */
	function _parenthesizedExpression() {
		$result = $this->_createTree('ptgParen', $this->_expression(), '');

		return $result;
	}

	/**
	 * It parses a term. It assumes the following rule:
	 * Term -> Fact [("*" | "/") Fact]
	 *
	 * @access private
	 * @return mixed The parsed ptg'd tree on success
	 */
	function _term() {
		$result = $this->_fact();
		while (($this->_current_token == "*") or ($this->_current_token == "/"))
		{
			/**/
			if ($this->_current_token == "*")
			{
				$this->_advance();
				$result2 = $this->_fact();
				$result = $this->_createTree('ptgMul', $result, $result2);
			}
			else
			{
				$this->_advance();
				$result2 = $this->_fact();
				$result = $this->_createTree('ptgDiv', $result, $result2);
			}
		}

		return $result;
	}

	/**
	 * It parses a factor. It assumes the following rule:
	 * Fact -> ( Expr )
	 *       | CellRef
	 *       | CellRange
	 *       | Number
	 *       | Function
	 *
	 * @access private
	 * @return mixed The parsed ptg'd tree on success
	 */
	function _fact() {
		if ($this->_current_token == "(")
		{
			$this->_advance(); // eat the "("
			$result = $this->_parenthesizedExpression();
			if ($this->_current_token != ")")
			{
				throw new PHPExcel_Writer_Exception("')' token expected.");
			}
			$this->_advance(); // eat the ")"
			return $result;
		}
		// if it's a reference
		if (preg_match('/^\$?[A-Ia-i]?[A-Za-z]\$?[0-9]+$/', $this->_current_token))
		{
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1 or Sheet1!$A$1 or Sheet1:Sheet2!$A$1)
		elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?[A-Ia-i]?[A-Za-z]\\$?[0-9]+$/u", $this->_current_token))
		{
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1 or 'Sheet1'!$A$1 or 'Sheet1:Sheet2'!$A$1)
		elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?[A-Ia-i]?[A-Za-z]\\$?[0-9]+$/u", $this->_current_token))
		{
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// if it's a range A1:B2 or $A$1:$B$2
		elseif (preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+:(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+$/', $this->_current_token) or preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+\.\.(\$)?[A-Ia-i]?[A-Za-z](\$)?[0-9]+$/', $this->_current_token))
		{
			// must be an error?
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// If it's an external range (Sheet1!A1:B2 or Sheet1:Sheet2!A1:B2 or Sheet1!$A$1:$B$2 or Sheet1:Sheet2!$A$1:$B$2)
		elseif (preg_match("/^" . self::REGEX_SHEET_TITLE_UNQUOTED . "(\:" . self::REGEX_SHEET_TITLE_UNQUOTED . ")?\!\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+:\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+$/u", $this->_current_token))
		{
			// must be an error?
			//$result = $this->_current_token;
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// If it's an external range ('Sheet1'!A1:B2 or 'Sheet1'!A1:B2 or 'Sheet1'!$A$1:$B$2 or 'Sheet1'!$A$1:$B$2)
		elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . "(\:" . self::REGEX_SHEET_TITLE_QUOTED . ")?'\!\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+:\\$?([A-Ia-i]?[A-Za-z])?\\$?[0-9]+$/u", $this->_current_token))
		{
			// must be an error?
			//$result = $this->_current_token;
			$result = $this->_createTree($this->_current_token, '', '');
			$this->_advance();

			return $result;
		}
		// If it's a number or a percent
		elseif (is_numeric($this->_current_token))
		{
			if ($this->_lookahead == '%')
			{
				$result = $this->_createTree('ptgPercent', $this->_current_token, '');
			}
			else
			{
				$result = $this->_createTree($this->_current_token, '', '');
			}
			$this->_advance();

			return $result;
		}
		// if it's a function call
		elseif (preg_match("/^[A-Z0-9\xc0-\xdc\.]+$/i", $this->_current_token))
		{
			$result = $this->_func();

			return $result;
		}
		throw new PHPExcel_Writer_Exception("Syntax error: " . $this->_current_token . ", lookahead: " . $this->_lookahead . ", current char: " . $this->_current_char);
	}

	/**
	 * It parses a function call. It assumes the following rule:
	 * Func -> ( Expr [,Expr]* )
	 *
	 * @access private
	 * @return mixed The parsed ptg'd tree on success
	 */
	function _func() {
		$num_args = 0; // number of arguments received
		$function = strtoupper($this->_current_token);
		$result = ''; // initialize result
		$this->_advance();
		$this->_advance(); // eat the "("
		while ($this->_current_token != ')')
		{
			/**/
			if ($num_args > 0)
			{
				if ($this->_current_token == "," or $this->_current_token == ";")
				{
					$this->_advance(); // eat the "," or ";"
				}
				else
				{
					throw new PHPExcel_Writer_Exception("Syntax error: comma expected in " . "function $function, arg #{$num_args}");
				}
				$result2 = $this->_condition();
				$result = $this->_createTree('arg', $result, $result2);
			}
			else
			{ // first argument
				$result2 = $this->_condition();
				$result = $this->_createTree('arg', '', $result2);
			}
			++$num_args;
		}
		if (!isset($this->_functions[$function]))
		{
			throw new PHPExcel_Writer_Exception("Function $function() doesn't exist");
		}
		$args = $this->_functions[$function][1];
		// If fixed number of args eg. TIME($i,$j,$k). Check that the number of args is valid.
		if (($args >= 0) and ($args != $num_args))
		{
			throw new PHPExcel_Writer_Exception("Incorrect number of arguments in function $function() ");
		}

		$result = $this->_createTree($function, $result, $num_args);
		$this->_advance(); // eat the ")"
		return $result;
	}

	/**
	 * Creates a tree. In fact an array which may have one or two arrays (sub-trees)
	 * as elements.
	 *
	 * @access private
	 *
	 * @param mixed $value The value of this node.
	 * @param mixed $left  The left array (sub-tree) or a final node.
	 * @param mixed $right The right array (sub-tree) or a final node.
	 *
	 * @return array A tree
	 */
	function _createTree($value, $left, $right) {
		return array('value' => $value, 'left' => $left, 'right' => $right);
	}

	/**
	 * Builds a string containing the tree in reverse polish notation (What you
	 * would use in a HP calculator stack).
	 * The following tree:
	 *
	 *    +
	 *   / \
	 *  2   3
	 *
	 * produces: "23+"
	 *
	 * The following tree:
	 *
	 *    +
	 *   / \
	 *  3   *
	 *     / \
	 *    6   A1
	 *
	 * produces: "36A1*+"
	 *
	 * In fact all operands, functions, references, etc... are written as ptg's
	 *
	 * @access public
	 *
	 * @param array $tree The optional tree to convert.
	 *
	 * @return string The tree in reverse polish notation
	 */
	function toReversePolish($tree = array()) {
		$polish = ""; // the string we are going to return
		if (empty($tree))
		{ // If it's the first call use _parse_tree
			$tree = $this->_parse_tree;
		}

		if (is_array($tree['left']))
		{
			$converted_tree = $this->toReversePolish($tree['left']);
			$polish .= $converted_tree;
		}
		elseif ($tree['left'] != '')
		{ // It's a final node
			$converted_tree = $this->_convert($tree['left']);
			$polish .= $converted_tree;
		}
		if (is_array($tree['right']))
		{
			$converted_tree = $this->toReversePolish($tree['right']);
			$polish .= $converted_tree;
		}
		elseif ($tree['right'] != '')
		{ // It's a final node
			$converted_tree = $this->_convert($tree['right']);
			$polish .= $converted_tree;
		}
		// if it's a function convert it here (so we can set it's arguments)
		if (preg_match("/^[A-Z0-9\xc0-\xdc\.]+$/", $tree['value']) and !preg_match('/^([A-Ia-i]?[A-Za-z])(\d+)$/', $tree['value']) and !preg_match("/^[A-Ia-i]?[A-Za-z](\d+)\.\.[A-Ia-i]?[A-Za-z](\d+)$/", $tree['value']) and !is_numeric($tree['value']) and !isset($this->ptg[$tree['value']]))
		{
			// left subtree for a function is always an array.
			if ($tree['left'] != '')
			{
				$left_tree = $this->toReversePolish($tree['left']);
			}
			else
			{
				$left_tree = '';
			}

			// add it's left subtree and return.
			return $left_tree . $this->_convertFunction($tree['value'], $tree['right']);
		}
		else
		{
			$converted_tree = $this->_convert($tree['value']);
		}
		$polish .= $converted_tree;

		return $polish;
	}

}
